The use of fiber composite tape laying machines for the manufacture of fiber composite parts is well known in the art. Such machines comprise a tape laying head mounted on the end of a cantilever arm that is supported for complex motion in order to apply fiber tape to a form or tool in order to create a part. The head normally travels in one direction along the tool and applies the fiber tape to the tool as it moves across the surface of the tool. The fiber tape comprises a resin matrix in which are embedded bundles of carbon fiber. The fiber tape is applied to a carrier layer of backing paper that is coated with a release agent. A feed reel on the head provides a supply of tape, and a take-up reel is provided to take up the backing paper after the fiber tape has been laid onto the part. Both reels are positively driven by reversible variable speed torque motors that are operated to maintain tension in the tape during the tape laying process. The drive of the tape is referred to as the U-axis of the machine, and although the reels are driven by the motors, the speed of deposition of the tape on the part is slightly greater than the speed that the tape comes off of the feed reel in order to maintain a positive tension in the tape during operation.
A compaction shoe on the head applies pressure to the backing paper to press the tape onto the part. The line of contact between the compaction shoe and the backing paper is called the line of compaction or the laydown line. As the fiber tape is pressed into the part at the laydown line the backing paper is separated from the fiber tape and proceeds along a tape path to the take-up reel. The head also includes a roller for pressing the fiber tape onto the part. The roller is mounted on a movable support and is normally out of contact with fiber tape while the tape is being pressed onto the part by the shoe. The roller is normally used to press the tail of a course of fiber tape onto the part, and for this reason is also called a tail compactor. The term “tail” refers to a less than full-width tapered end of a course of fiber tape. Movement of the roller into contact with the fiber tape causes the shoe to retract from pressing engagement with the tape. The roller is positioned on the head so that it does not press on the fiber tape through the backing paper, it presses directly on fiber tape after the backing paper has been stripped from the fiber tape. After the roller is interchanged with the shoe, the laydown line of the roller is at the same position as the laydown line of the shoe. Whether the compaction shoe or the roller is used to lay the fiber tape, the tape head always moves forward, from upstream to downstream on the tool or part, and with the feed reel leading the take-up reel. Although the tape head lays tape in the part while traveling back and forth across the part, the head reverses its orientation 180 degrees on the cantilever arm in order to do so. As a result, the tape head never lays fiber tape while moving from downstream to upstream on the part, or with the take-up reel leading the feed reel.
The head also includes a heater for heating the resin just before it is applied to the tool or the part. The entire operation of the tape laying machine is under CNC control. U.S. Pat. Nos. 4,557,783, 5,314,563, and 5,352,306, all presently assigned to the assignee of the present invention, disclose in greater detail composite tape laying heads as described above.
The fiber composite tape itself is used in discrete widths Common nominal tape widths presently used include 75 mm, 150 mm, 300 mm, 3 inch, 6 inch, and 12 inch, but other widths are possible. As a result, the laying up of an aircraft component such as a control surface or a wing requires many passes of the tape head over the part, and several hours of time. In order to manufacture a part to the exacting standards required by the aircraft industry, the angle on the end of the tape has to be cut to exactly match the angle on the edge of the part to which the tape is being applied. The tape head contains a knife cutter and a suitable mechanism is provided on the tape head to cut the tape end to any desired angle. Trimming the tape end to the desired angle may produce a section of tape that is scrap. The scrap must be removed from the tape so that it will not be laid in the part. To remove the scrap, the normal procedure is to maneuver the tape head to a scrap area where the scrap can be removed from the backing paper by depositing it in the scrap area. The tape head is then returned to the part and the freshly trimmed tape end is laid on the edge of the tool or part in position to begin to lay the next course of tape. Since the tape laying machine is under computer control, once the shape of the part and the desired tape courses have been programmed into the computer, the tape laying machine can run for several hours without operator intervention.
The tape pattern that is to be laid on the part may require the use of a length or course of tape that has a width that is less that the full width of the tape. Such a tape course is called a non-full width course. Non-full width courses present special problems. A fractional width of the tape adjacent to the non-full width course has to be removed from the backing paper by being laid in the scrap area in order to form the non-full width course. U.S. Pat. Nos. 4,978,417, 5,114,519 and 5,115,993 are directed to methods and apparatus for removing scrap from around non-full width courses. At times, scrap that is supposed to be laid in the scrap area remains on the backing paper and ends up getting laid in the part. Other times, the non-full width course is prematurely removed from the backing paper with the scrap and is laid in the scrap area, and does not get laid in the part. Either event causes a manufacturing defect in the part which may render the part unsafe.
Accordingly, it would be desirable to develop a reliable process for removing scrap portions from fiber tape to ensure that the scrap is removed from the tape in the scrap area and not deposited in the part.